Apoptosis is a morphologically distinct form of programmed cell death that is important in the normal development and maintenance of multicellular organisms. Dysregulation of apoptosis can take the form of inappropriate suppression of cell death, as occurs in the development of some cancers, or in a failure to control the extent of cell death, as is believed to occur in acquired immunodeficiency and certain neurodegenerative disorders, such as spinal muscular atrophy (SMA).
Childhood spinal muscular atrophies are neurodegenerative disorders characterized by progressive spinal cord motor neuron depletion and are among the most common autosomal recessive disorders (Dubowitz, V. 1978, Brooke, M. A. 1986). Type I SMA is the most frequent inherited cause of death in infancy. The loss of motor neurons in SMA, has led to suggestions that an inappropriate continuation or reactivation of normally occurring motor neuron apoptosis may underlie the disorder (Sarnat, H. B. 1992). NAIP, a gene associated with SMA, has been mapped to human chromosome 5q13.1
Some baculoviruses encode proteins that are termed inhibitors of apoptosis proteins (IAPs) because they inhibit the apoptosis that would otherwise occur when insect cells are infected by the virus. These proteins are thought to work in a manner that is independent of other viral proteins. The baculovirus IAP genes include sequences encoding a ring zinc finger-like motif (RZF), which may be involved in DNA binding, and two N-terminal domains that consist of a 70 amino acid repeat motif termed a BIR domain (Baculovirus IAP Repeat).